The present invention relates to a method and apparatus for controlling a production line, in which a final product is obtained by performing a plurality of process steps on at least one product. The present invention also relates to a computer readable storage medium in which a production line control program is stored.
Examples of the production line for obtaining a final product by performing a plurality of process steps on at least one product include a semiconductor device production line. In a semiconductor device production line, a semiconductor device is obtained as a final product by sequentially performing a plurality of process steps on a wafer in which a plurality of semiconductor chips are formed. The production line herein includes both a mass-production line and a development line.
The operating frequency of a semiconductor device as a final product is one of the known parameters representing the performance required for the semiconductor device. The value of a semiconductor device greatly depends on the performance (e.g., the operating frequency, in particular) thereof. Accordingly, the higher the operating frequency of a semiconductor device, the more valuable the device will be. And in order to produce a semiconductor device having a high operating frequency, a new semiconductor process enabling the reduction of a minimum process size should be introduced.
As a result of a semiconductor device production line, some of the semiconductor devices belonging to a single lot might have IC wiring patterns of sizes exceeding the tolerance range of other semiconductor devices belonging to the lot. Also, a semiconductor device belonging to a lot might have an IC wiring pattern of a much different size than that of a semiconductor device belonging to another lot. Such variation in the sizes of wiring patterns seriously affects the operating frequencies of semiconductor devices. For example, variation in the gate lengths of gate electrodes of transistors considerably affects the operating frequencies of the semiconductor devices including the transistors.
Thus, in accordance with a conventional method for controlling a semiconductor device production line, every time a single process step for a single lot is finished, the sizes of the wiring patterns for semiconductor integrated circuits included in the lot are measured. If any of the measured sizes of the wiring patterns is out of a predetermined range, a wafer including devices of such a size or a lot including such a wafer is removed from the production line. In addition, the processing conditions for the process step, during which devices of such an undesired size are formed, are also re-examined, thereby performing a feedback control.
Moreover, after all of the process steps on a semiconductor chip are finished, the semiconductor device is tested as a final product to determine whether or not the semiconductor device operates normally, at what megahertz the semiconductor device operates and so on. And based on the results of these tests on products, the price of each semiconductor device is set according to the rank of the operating frequency of the semiconductor device. Alternatively, if there are any semiconductor devices operating at too low a frequency to be valuable as a product, then such devices are thrown away as defective products.
However, it is now difficult to apply such a conventional control method to the production line of semiconductor devices belonging to a deep sub-micron generation. This is because the sizes of wiring patterns are different from each other to a far larger degree among semiconductor devices belonging to a single lot or between semiconductor devices belonging to mutually different lots. Under such circumstances, even semiconductor devices produced by a single production line might have mutually different operating frequencies.
If the operating frequencies of semiconductor devices are distributed in such a wide range, various inconveniences are caused in drawing up a project. For example, since it is difficult to precisely expect how many products can be produced and how valuable those product can be, it is hard to draw up a production plan. Also, if the operating frequency of a semiconductor device produced by a process of a brand new generation is at almost the same level as that of a semiconductor device produced by a process of a previous generation, the value of the new semiconductor device is lower than expected. In such a case, in spite of the implementation of a brand new process, the resulting product cannot be so valuable as to compensate for the investment.
In view of these problems, the present invention was made to (1) expect the number of products estimatingly finished for each performance rank of the final products before the products are finished, and (2) modify the performance of a resulting final product during a plurality of process steps performed on a product.
In order to accomplish these objects, a first method according to the present invention involves controlling a production line, in which a final product is obtained by performing a plurality of process steps on each of a plurality of products. The method includes the steps of: obtaining measured data by measuring the characteristics of a product at a time a particular one of the process steps, performed on the product, is finished; expecting the performance of a final product based on the measured data; and calculating a first number of products, estimatingly finished for each performance rank thereof, based on the performance of the final product expected in the step of expecting.
In accordance with the first production line control method, the performance of a final product is expected based on the measured data obtained by measuring the characteristics of a product at a time one of the process steps, performed on the product, is finished. And the number of products, estimatingly finished for each performance rank thereof, is calculated based on the expected performance of the final product. Accordingly, the number of final products can be expected for each performance rank thereof at a time a particular process step is finished. That is to say, before each product is finished, it is possible to expect the number of products capable of being produced and the cost of the products. As a result, a production plan can be drawn up more easily.
In one embodiment of the present invention, the step of expecting preferably includes the step of expecting the performance of the final product based on measured data obtained at a time another one of the process steps, performed prior to the particular process step, was finished and the measured data obtained at the time the particular process step is finished.
In such an embodiment, the performance of a final product can be expected more accurately. Accordingly, the number of final products can be expected more accurately for each performance rank.
In another embodiment of the present invention, the step of expecting preferably includes the step of expecting the performance of the final product based on measured data obtained at a time another one of the process steps was finished, performed prior to the particular process step, the measured data obtained at the time the particular process step is finished, and expected data estimatingly obtained at a time still another one of the process steps is finished, to be performed posterior to the particular process step.
In such an embodiment, the performance of a final product can be expected even more accurately. Accordingly, the number of final products can be expected even more accurately for each performance rank.
In still another embodiment of the present invention, the plurality of process steps are preferably performed on each of a plurality of lots, the plurality of products separately belonging to the respective lots. The method preferably farther includes the steps of: expecting a date of completion on which all of the process steps on the products belonging to one of the lots would be completed; obtaining a second number of products, estimatingly finished for each said performance rank by a due date, based on the date of completion and the first number; and if the second number runs short of a required number, performing the process steps on another one of the lots, which produces final products of the same performance rank as the products estimatingly finished by the due date, at a higher rate.
In such an embodiment, if the number of products estimatingly finished for each performance rank by a due date runs short of a required number, then the process steps on another lot, which can produce final products of the same performance rank as the products estimatingly finished by the due date, are performed at a higher rate. Accordingly, it is possible to reduce or eliminate the shortage in number of products finished for each performance rank by a due date.
In still another embodiment, the first method preferably further includes the steps of: expecting a date of completion on which all of the process steps on at least one of the products would be completed; obtaining a second number of products, estimatingly finished for each said performance rank by a due date, based on the date of completion and the first number; and if the second number runs short of a required number, introducing products into the production line to produce final products of the same performance rank as the products estimatingly finished by the due date.
In such an embodiment, if the number of products estimatingly finished for each performance rank by a due date runs short of a required number, then products are introduced into the production line to produce final products of the same performance rank as the products estimatingly finished by the due date. Accordingly, it is possible to reduce or eliminate the delay of production.
In still another embodiment, the first method preferably further includes the steps of: expecting a date of completion on which all of the process steps on at least one of the products would be completed; obtaining a second number of products, estimatingly finished for each said performance rank by a due date, based on the date of completion and the first number; and if the second number runs short of a required number, modifying processing conditions for the process steps to be performed on the at least one product posterior to the particular process step such that the performance of the final product is improved.
In such an embodiment, if the number of products estimatingly finished for each performance rank by a due date runs short of a required number, the number of final products of the same performance rank as that of the products estimatingly finished by the due date can be increased. Accordingly, it is possible to reduce or eliminate the shortage in number of products finished for each performance rank by a due date.
In still another embodiment, the first method preferably farther includes the steps of: expecting a date of completion on which all of the process steps on at least one of the products would be completed; obtaining a second number of products, estimatingly finished for each said performance rank by a due date, based on the date of completion and the first number; and if the second number runs short of a required number, additionally performing a new process step on the at least one product posterior to the particular process step such that the performance of the final product is improved.
In such an embodiment, if the number of products estimatingly finished for each performance rank by a due date runs short of a required number, the number of final products of the same performance rank as that of the products estimatingly finished by the due date can be increased. Accordingly, it is possible to reduce or eliminate the shortage in number of products finished for each performance rank by a due date.
In still another embodiment, the plurality of process steps are preferably performed on each of a plurality of lots, the plurality of products separately belonging to the respective lots. The first method preferably further includes the steps of: expecting a date of completion on which all of the process steps on the products belonging to one of the lots would be completed; obtaining a second number of products, estimatingly finished for each said performance rank by a due date, based on the date of completion and the first number; and if the second number is in excess of a required number, performing the process steps on another one of the lots, which produces final products of the same performance rank as the products estimatingly finished by the due date at a lower rate.
In such an embodiment, if the number of products estimatingly finished for each performance rank by a due date is in excess of a required number, the number of final products of the same performance rank as that of the products estimatingly finished by the due date can be reduced. Accordingly, it is possible to reduce or eliminate the excess in number of products finished for each performance rank by a due date. And it is also possible to finish products belonging to another rank on an earlier date.
In still another embodiment, the plurality of process steps are preferably performed on each of a plurality of lots, the plurality of products separately belonging to the respective lots. The first method preferably further includes the steps of: expecting a date of completion on which all of the process steps on the products belonging to one of the lots would be completed; obtaining a second number of products estimatingly finished for each said performance rank by a due date, based on the date of completion and the first number; and if the second number is in excess of a required number, stopping the process steps on another one of the lots, which produces final products of the same performance rank as the products estimatingly finished by the due date.
In such an embodiment, if the number of products estimatingly finished for each performance rank by a due date is in excess of a required number, the number of final products of the same performance rank as that of the products estimatingly finished by the due date can be reduced. Accordingly, it is possible to reduce or eliminate the excess in number of products finished for each performance rank by a due date. And it is also possible to finish products belonging to another rank on an earlier date.
In still another embodiment, the first method preferably farther includes the steps of: expecting a date of completion on which all of the process steps on at least one of the products would be completed; obtaining a second number of products estimatingly finished for each said performance rank by a due date based on the date of completion and the first number; and if the second number is in excess of a required number, omitting at least one of the process steps performed posterior to the particular process step.
In such an embodiment, if the number of products estimatingly finished for each performance rank by a due date is in excess of a required number, the number of final products of the same performance rank as that of the products estimatingly finished by the due date can be reduced. Accordingly, it is possible to reduce or eliminate the excess in number of products finished for each performance rank by a due date. And it is also possible to finish products belonging to another rank on an earlier date.
In still another embodiment, the plurality of process steps are preferably performed on each of a plurality of lots, the plurality of products separately belonging to the respective lots. The first method preferably further includes the steps of: obtaining estimated profit to be procured by each said lot based on the number of products estimatingly finished, production costs and selling price for each said performance rank of the final products; and performing the process steps on the products belonging to a lot for which the profit obtained is relatively high, at a higher rate.
In such an embodiment, the products, which are estimated to procure relatively high profit, can be finished earlier. Accordingly, it is possible to increase the profitability of a production line.
In still another embodiment, the first method preferably further includes the steps of: determining whether or not the performance of the final product expected in the step of expecting meets a predetermined standard; and removing products of which the final products are determined as not meeting the predetermined standard from the production line.
In such an embodiment, defective products not meeting a predetermined standard are not produced in vain.
In still another embodiment, the plurality of process steps are preferably performed on each of a plurality of lots, the plurality of products separately belonging to the respective lots. The first method further includes the step of transferring products belonging to one of the lots to another lot to which other products belong, the final products of which would be of approximately the same performance rank as that of the performance expected in the step of expecting.
In such an embodiment, the performance of final products can be averaged among the lots. Accordingly, the work of increasing/decreasing the number of final products having a particular performance can be easily done.
A second method according to the present invention involves controlling a production line in which a final product is obtained by performing a plurality of process steps on a product. The second method includes the steps of: obtaining measured data by measuring the characteristics of a product at a time a particular one of the process steps performed on the product is finished; comparing the measured data to a reference value of the characteristics of the product; and if the measured data is inferior to the reference value, modifying processing conditions for at least one of the process steps to be performed posterior to the particular process step such that the performance of the final product is improved.
In accordance with the second production line control method, measured data obtained by measuring the characteristics of a product, on which a particular process step has been performed, is compared to a reference value of the characteristics of the product. And if the measured data is inferior to the reference value, processing conditions for at least one process step to be performed posterior to the particular process step are modified such that the performance of a final product is improved. Accordingly, the performance of the final product can be superior to the performance expected at a time the particular process step is finished. As a result, it is possible to produce a larger number of final products having higher performance.
A third method according to the present invention involves controlling a production line in which a final product is obtained by performing a plurality of process steps on a product. The third method includes the steps of: obtaining measured data by measuring the characteristics of a product at a time a particular one of the process steps performed on the product is finished; comparing the measured data to a reference value of the characteristics of the product; and if the measured data is inferior to the reference value, adding a new process step posterior to the particular process step such that the performance of the final product is improved.
In accordance with the third production line control method, measured data obtained by measuring the characteristics of a product on which a particular process step has been performed is compared to a reference value of the characteristics of the product. And if the measured data is inferior to the reference value, a new process step is added such that the performance of the final product is improved. Accordingly, the performance of the final product can be superior to the performance expected at a time the particular process step is finished. As a result, it is possible to produce a larger number of final products having higher performance.
A fourth method according to the present invention involves controlling a production line in which a final product is obtained by performing a plurality of process steps on a product. The fourth method includes the steps of: obtaining measured data by measuring the characteristics of a product at a time a particular one of the process steps performed on the product is finished; comparing the measured data to a reference value of the characteristics of the product; and if the measured data is superior to the reference value, omitting at least one of the process steps to be performed posterior to the particular process step.
In accordance with the fourth production line control method, measured data obtained by measuring the characteristics of a product on which a particular process step has been performed is compared to a reference value of the characteristics of the product. And if the measured data is superior to the reference value, at least one process step to be performed posterior to the particular process step is omitted. Accordingly, the number of process steps can be reduced without deteriorating the performance of a final product from the initially expected performance. As a result, the final product can be produced earlier than initially scheduled.